I. Field of the Invention
This invention relates to the manufacturing of lead storage batteries, specifically to the step of casting-on battery straps and posts to rows of positive and negative lugs of groups of battery elements.
II. Description of the Prior Art
A modern lead storage battery starts with a battery case having cells formed therein by partitions or walls located within the battery case. Within each cell there is located a series of battery plates and separators which together form a group. The battery plates comprise positive and negative grid-like plates, which are coated with a lead oxide paste to give the battery the potential of holding the electric charge. The plates are of positive and negative character and alternate in sequence. Separators are positioned between each of the plates to isolate them from one another. Before the group is formed and placed in the cell, the plates and separators are arranged into a stack, each of the plates having an extension called a lug on one end, the positive lugs forming a row on one side of the stack and the negative lugs forming a row on the opposite side. The row of positive lugs must be connected together, and the row of negative lugs must be connected together to form the group. Several methods have evolved over the years for accomplishing this task, and a popular method is known as the cast-on method where the stacks of battery plates are carried over and lowered into a mold having a suitable channel to receive the rows of positive and negative lugs. The channels are filled with molten lead which surrounds the rows of lugs and when the lead solidifies, the lugs are molded together to form a casting known as a battery strap.
Each of the groups within the battery cells must be connected together either by connecting over or through the battery partition walls. In order to accomplish this, one end of the strap is molded to include an extension known as an intermediate post or intermediate lug. In the intercell method the intermediate posts are lined up on each side of the partitions and a connection is made between the intermediate posts through apertures in the partition walls. To facilitate a good connection, the faces of the posts facing each other with the battery partition in between are substantially flat and parallel.
The Farmer U.S. Pat. No. 3,604,094 describes a casting station in a battery element fabricating machine. The casting station comprises a mold block and dams which are mounted at the top of the mold block. The dams have recesses or cavities for receiving the molten lead which will be cast as the strap portions on the battery groups. In addition, mold recesses are provided in the mold block adjacent to, and in communication with, the strap cavities so that the post portions will be integrally cast with the straps. FIGS. 6 and 7 show the mold block 124; the dams 126; the dam recesses or cavities 127; and post recesses 128 and 129.
In FIG. 7 of the Farmer U.S. Pat. No. 3,616,845, a molding station is described comprising a mold block 94 having a strap portion cavity 142 and a post portion cavity 144. The remaining portion of the cavity is formed by a movable wall 146 having a flat surface 150 with a recession 148 therein. The recession 148 acts to form a projecting stud on the face of the post portion of the casting. The wall 146 is movable away from the face of the casting at the time when the casting is to be removed from the mold. This wall is pivotable away from the casting so that the projecting stud can be removed along with the casting.
Other U.S. patents dealing with the casting of straps and posts on the groups of insulated battery plates are the Vieth U.S. Pat. No. 2,799,905 and the Lutz U.S. Pat. No. 700,959.
One of the problems which has been encountered in casting on the straps and posts to a battery stack is that the endmost plate lug when inserted into the mold channel for casting, may be engaged by lead only on one side and its edges since one face or side of that lug is pressed firmly up against a flat end of the mold and does not otherwise cast to the remaining portion of the strap. While upon removal of the group or element from the cast-on operation it might first appear that the strap of the battery group or element did integrally fuse with the battery lugs, including the lug of the endmost plate, it is found that, upon subsequent processing, these endmost plate lugs have a tendency to crack or peel away from the remainder of the group element and to otherwise exhibit somewhat inferior properties.
Another problem which arises is the formation of unwanted projections on the face of the post portion of the strap casting, the projection being a result of overfilling of the cavity with molten lead. In particular, the formation of these projections would prevent the face of the post from being connected to an adjacent intermediate post through the battery partition.